Stimulation procedures often require the use of well treating materials having high compressive strength. In hydraulic fracturing, such materials must further be capable of enhancing the production of fluids and natural gas from low permeability formations. In a typical hydraulic fracturing treatment, fracturing treatment fluid containing a solid proppant is injected into the wellbore at high pressures. Once natural reservoir pressures are exceeded, the fluid induces fractures in the formation and proppant is deposited in the fracture, where it remains after the treatment is completed. The proppant serves to hold the fracture open, thereby enhancing the ability of fluids to migrate from the formation to the wellbore through the fracture. Because fractured well productivity depends on the ability of a fracture to conduct fluids from a formation to a wellbore, fracture conductivity is an important parameter in determining the degree of success of a hydraulic fracturing treatment. Choosing a proppant is critical to the success of well stimulation.
The prior art has been principally focused on the development of spherical well treating particulates. For example, manufactured ceramic proppants have been reported as requiring a sphericity value of about 0.70 or greater. See, for instance, Krumbein et al, Stratiography and Sedimentation, W. H. Freeman and Co., 1955. The requirement that well treatment particulates, such as proppants, be spherical particulates may be attributed to the perception that spherical particulates achieve the highest possible conductivity throughout the proppant pack and allow for the highest permeability for a uniform shape.
Proppants used in the art include sand, glass beads, walnut hulls, and metal shot as well as resin-coated sands, intermediate strength ceramics, and sintered bauxite; each employed for their ability to cost effectively withstand the respective reservoir closure stress environment. The relative strength of these various materials increases with their corresponding apparent specific gravity (ASG), typically ranging from 2.65 for sands to 3.6 for sintered bauxite. Unfortunately, increasing ASG leads directly to increasing degree of difficulty with proppant transport and reduced propped fracture volume, thereby reducing fracture conductivity.
More recently, ultra lightweight (ULW) materials have been used as proppants since they reduce the fluid velocity required to maintain proppant transport within the fracture, which, in turn, provides for a greater amount of the created fracture area to be propped. Such ULW proppants, like conventional heavier proppants, have the capability to effectively withstand reservoir closure stress environments while increasing fracture conductivity. While offering excellent compressive strength, ULW proppants often soften and loose their compressive strength especially at high temperature and high pressure downhole conditions. Alternatives have therefore been sought.
Improved well treating particulates have also been sought for use in the prevention of sand grains and/or other formation fines from migrating into the wellbore. When such migration occurs, such grains and fines typically reduce the rate of hydrocarbon production from the well. In addition, such grains and fines can cause serious damage to well tubulars and to well surface equipment.
Gravel packs are often used to control migration of particulates in such producing formations. A gravel pack typically consists of a uniformly sized mass of spherical particulates which are packed around the exterior of a screening device. Such screening devices, typically positioned in an open hole or inside the well casing, have very narrow openings which are large enough to permit the flow of formation fluid but small enough to allow the particulates to pass through. The particulates operate to trap, and thus prevent the further migration of, formation sand and fines which would otherwise be produced along with the formation fluid.
In order to be useful in gravel packing applications, such particulates must exhibit high strength and be capable of functioning in low permeability formations. While ULW well treating agents have been proposed for use in gravel packing applications to improve transport, placement, and packing efficiency, concerns exist however that ULW particulates do not demonstrate the chemical resistance properties required of particulates for use in gravel packing.
Alternative well treating agents have therefore been sought which exhibit high compressive strength and which may be used to improve packing efficiency, transport and placement of proppant in fracturing. It is further desired that such materials be useful in other oilfield treatment processes, such as sand control.
In addition, alternative proppants which are capable of increasing fracture width as well as conductivity are desired.
It is further desired that alternative well treatment particulates be capable of providing a chemical treatment agent to the wellbore and formation in order to inhibit deleterious conditions which may typically develop. Oilfield fluids (e.g., oil, gas, and water) are complex mixtures of aliphatic hydrocarbons, aromatics, hetero-atomic molecules, anionic and cationic salts, acids, sands, silts, clays and a vast array of other components. The nature of these fluids combined with the severe conditions of heat, pressure, and turbulence to which they are often subjected during retrieval, are contributory factors of unwanted deposition of substances which may be responsible for decreasing the permeability of the subterranean formation as well as reducing well productivity and shortening of the lifetime of production equipment. Such may include paraffin deposition (including the precipitation of wax crystals), formation of water-in-oil as well as oil-in-water emulsions, gas hydrate formation and corrosion and asphaltene precipitation. In order to rid such unwanted deposits and precipitates from wells and equipment, it is necessary to stop the production which is both time-consuming and costly.
An especially troublesome unwanted deposits are paraffin hydrocarbon waxes which tend to precipitate and crystallize at low temperatures, thereby causing oil to lose its fluidity. Over a range of temperatures, these paraffin wax crystals continue to aggregate and may even solidify the oil. This creates difficulties in transporting the petroleum fuel or crude oil through flow lines, valves, and pumps. Paraffin wax crystals are particularly problematic at lower temperatures and in colder climates where, as the temperature drops and approaches the crude oil's pour point, the transportation of crude oil becomes more difficult. Once out of solution, paraffin wax crystals often plug flow lines, production tubing, flow lines, screens and filters.
Various well treatment agents are often used in production wells to prevent the deleterious effects caused by the formation and precipitation of unwanted materials. For instance, pour point depressants and wax crystal modifiers have been used to change the nature of wax crystals that precipitate from the petroleum fuel or crude oil, thereby reducing the tendency of wax crystals to set into a gel.
It is essential that such well treatment agents be placed into contact with the oilfield fluids contained in the formation before such fluids enter the wellbore where deleterious effects are commonly encountered. Several methods are known in the art for introducing such well treatment agents into production wells. A principal disadvantage of such prior art methods is the difficulty in releasing the well treatment agent into the well over a sustained period of time. As a result, treatments must repeatedly be undertaken to ensure that the requisite level of well treatment agent is continuously present in the well. Such treatments result in lost production revenue due to down time.
Treatment methods are therefore sought for introducing well treatment agents into oil and/or gas wells wherein the well treatment agent may be released over a sustained period of time. It is desired that such methods not require continuous attention of operators over prolonged periods.